1. Field of the Invention
The present invention relates to a calibration method for an acceleration sensor in a storage device and a storage device, for correcting a position of an actuator by detecting an acceleration of an enclosure in the storage device for reading or reading/writing data by a head from and to a storage medium.
2. Description of the Related Art
A storage disk device such as a magnetic disk device etc is widely utilized as a storage device for a computer etc. a high density record and a speed-up are requested of this type of storage disk device.
FIG. 10 is a diagram showing a construction of a magnetic disk device in the prior art. FIG. 11 is an explanatory diagram showing residual vibrations of an enclosure.
As shown in FIG. 10, the magnetic disk device includes a magnetic disk 91 and a magnetic head 92. The magnetic head 92 reads and writes data from and to the magnetic disk 91. An actuator 93 supports the magnetic head 92. A VCM (voice coil motor) 94 drives the actuator 93. An enclosure 90 holds those components inside.
In the thus constructed magnetic disk device, the actuator 93 mounted with the magnetic head 92 seeks the head 92 from a certain track to another target track. This is called a seek operation. A high-speed respondency is obtained reducing this seek time.
The acceleration and deceleration of the actuator 93 are intensified for reduce the seek time. At this time, a force acts upon the whole enclosure 90 of the disk device due to reaction of the actuator 93. The enclosure 90 is normally fixed, and therefore it does not mean that the enclosure 90 is vibrated by the reaction as it is. A mechanical transfer function thereof, however, has a point of resonance at a given frequency. Therefore, as shown in FIG. 11, when the enclosure 90 is excited by the seek reaction, a vibration of the enclosure 90 remains after the seek operation.
This vibration is applied to a head position signal as a relative deviation between the head 92 and the disk medium 91, and hence appears as a residual vibration in the position signal after the seek. Consequently, the seek time elongates. One of the basic countermeasures is to enhance a capability of restraining an error signal by improving a servo control characteristic. When a track pitch on the disk is narrowed, however, it can not cope with this simply by a servo gain enhancement. Further, the vibration of the enclosure is on the order of several hundreds Hz which can not be essentially compressed by a normal servo system of the magnetic disk.
In a prior system, as shown in FIG. 10, acceleration sensors 95, 96 for detecting an acceleration of the enclosure 90 are provided for directly measuring the acceleration of the enclosure 90. Then, there is proposed a feed forward system for correcting the servo control signal by the measured signal. This type of system is disclosed in, e.g., Japanese Patent Application Laid-Open Publication No.9-45024, U.S. Pat. No. 5,299,075, U.S. Pat. No. 5,426,545 and U.S. Pat. No. 5,663,847.
There arise, however, the following problems inherent in the prior art.
(1) It is required that a sensitivity of the acceleration sensor be obtained in order to use the acceleration sensor and utilize this sensor for the position control. There is, however, the sensitivity of the acceleration sensor is different in each sensor. For example, in piezoelectric sensors, there is .+-.20% difference in the sensitivity. Accordingly, a problem is that a preferable output can not be obtained even by setting a fixed sensitivity.
(2) There is a method of selecting parts which have been calibrated beforehand. However, a problem is that the cost increases. Further, the sensitivity on a state of being loaded into the device might differ from the detected sensitivity on a state of the parts. Therefore, there arises such a problem that a calibrated value on the state of the parts can not be used as it is.